Electric transformer substations are basically formed by three essential elements or parts or functional units, though functionally independent from one another, one of which parts consists of high-voltage switchgear, whereas a second part consists of a transformer, the third part being formed by a low-voltage switchboard, such that these parts are independent and are electrically connected. In this sense, in said transformer substations in which the functional units are independent, each of them has independent insulation and cooling means that is not shared with other units.
According to a common configuration, high-voltage switchgear comprise a line connection and an outgoing feeder, forming a loop, as well as a third protection position supplying the transformer, from which the low-voltage electric power in turn exits, this outgoing feeder of the transformer being connected to the low-voltage switchboard or module having the corresponding bases for the connection of outgoing feeder cables for the distribution and corresponding low-voltage power supply of the installation or building in question.
The transformer substation is supplied through the high-voltage line connection of the first feeder switchgear, which is connected, through the outgoing feeder of the loop, with the second feeder switchgear, which allows isolating a building or an installation without the power supply to the remaining installations being cut off as a result. The electric power is led from this second feeder switchgear to the next transformer substation, which will logically supply another installation.
The transformer is supplied through the third position or switchgear, carrying out the electric connection between both elements by means of external cables, as is shown, for example, in patents ES2228264B2, EP1267367A1, FR2881001B1, FR2826194B1, FR2905532A1 and DE9202127U1, which are exposed, being able to lead to unwanted breakdowns and accidents. Furthermore, this wiring must be carried out “in situ”, which requires specialized operators for correctly carrying out the various connections. Specifically, the connections between the high-voltage switchgear and the transformer are carried out by means of cables with terminals at their ends, the terminals usually being constructed at the building site, therefore they are not subjected to the relevant tests to check the quality of the coupling.
The connection between the transformer and the switchgear can also be carried out by means of a direct connection without using cables, as is shown, for example, in patents ES2155037B1, EP1326313A1, WO2004012312A1, WO03032458A1, WO02075757A1 and FR2782418B1.
The third position, referred to as protection switchgear, incorporates protection of the transformer, usually by means of fuses or even by means of a circuit breaker. These fuses are usually installed inside the high-voltage switch gear, but there are also solutions in which they are integrated in the tank itself of the transformer, immersed in the oil itself of the transformer, or inside a bay independent of the high-voltage switch gear and the transformer, as defined for example in patent FR2782418B1.
The function of said fuses is to prevent electric failures that may occur downstream, i.e., in the low-voltage distribution network, in the low-voltage switchboard, in the high-voltage interconnection or in the transformer, from affecting the substation, thus limiting the extent of the incident.
In this sense, patent FR2782418B1 protects both embodiments with regard to the arrangement of the fuses, both inside the tank of the transformer and inside a bay independent from the high-voltage switch gear and the transformer. In each of the embodiments of said patent, the fuses are accompanied by a breaker, which is also arranged together with the fuses inside the tank of the transformer or inside the mentioned independent bay. In the first case, the fuses and the breaker are insulated in the dielectric liquid itself of the transformer, and in the second case, in a dielectric gas comprised in the mentioned bay. In this latter case, the bay is assembled on the cover of the transformer and on the high-voltage switch gear, the transformer—bay—high-voltage switchgear interconnection being carried out by means of bushings comprised in the transformer, the mentioned bay and the high-voltage switch gear. Therefore, this French patent uses the interconnection between transformer and high-voltage switch gear to include in it part of the protection of the transformer substation, which in the remaining mentioned patent examples is included inside the switchgear or high-voltage switch gear, except in WO03032458A1. In a possible embodiment of this last patent document, part of the protective elements, such as fuses, is also arranged inside an independent protection module.
The assembly determined by the high-voltage switchgear, the transformer and the low-voltage switchboard are usually arranged in a closed room which, in most cases, corresponds to the basement or storage area of the building which is to be supplied, or else in a shed outside and close to the building, which must offer sufficient safety and ergonomic conditions for operators, made in suitable accesses or spaces appropriate for the operation and installation of the equipment.
The main requirement with respect to space is the need to have a clear front of approximately one meter wide both in the high-voltage switch gear and in the low-voltage switch gear, as well as an access corridor and safety distances to elements which are energized and can be accessible by operators or third persons. This means that in practice, a large amount of space is necessary for the placement of all the components of the substation, which involves an enormous cost for the power supply company. This is why there is great interest today in compact equipment which occupies increasingly smaller spaces.
In this sense, the solution of patent FR2782418B1 involves the drawback that due to installing the fuses inside the transformer, this transformer has larger dimensions and therefore occupies greater space than a conventional transformer does. The same space problem is involved in the case in which the fuses are installed inside a bay which is assembled on the cover of the transformer and on the high-voltage switch gear, because yet another projection is added to the transformer substation. Furthermore, due to the dielectric medium used in said bay and therefore due to the insulation distances to be respected between phases, said bay can occupy considerable space, and accordingly the transformer substation can be bulkier. Likewise, due to using a gas as a dielectric medium in said bay, in the event that any of the fuses melts, said bay must be replaced with a new one, which entails in addition to the disassembly of said bay, draining the internal gas, this gas being a toxic gas and it can contribute to the greenhouse effect, so a more complicated, more expensive and more meticulous replacement process is required.
Likewise, the solution of patent FR2782418B1 involves the drawback that due to installing the high-voltage and low-voltage switch gear on a vertical plane of the transformer, the cooling fins corresponding to said vertical side or plane of the transformer are eliminated, which involves reducing the useful cooling surface of the transformer, and therefore the increase of the operating temperature thereof. The same problem is repeated in the solution of ES2155037B1.
In relation to the transformers used in the solutions of WO03032458A1, WO02075757A1 and ES2155037B1, these transformers are “special” transformers because in the solution in WO02075757A1, the low-voltage bushings are arranged in a vertical side of the transformer, whereas in the case of the solution in ES2155037B1, both the low-voltage and the medium-voltage bushings are arranged in a vertical side. This configuration of the transformer complicates the assembly tasks during its manufacture because in the operation of cribbing a “standard” transformer, all the elements thereof (windings, magnetic circuit, bushings, etc.) are secured to the cover itself of the transformer, all the necessary electric connections between the elements being carried out beforehand, and they are introduced in the tank once the cover is in place in order to then screw said cover to the tank and subsequently fill it with oil. In this sense, in the case of WO02075757A1 and ES2155037B1, the assembly operations are complicated due to the complexity of carrying out the connections inside the tank between the bushings and the windings.
In the state of the art, as is shown in the mentioned patent examples, in which the interconnection between the transformer and the high-voltage switchgear is used to include part of the protection of the transformer substation, said part of the protection is formed by the fuses and the breakers or switches. The remaining elements forming the protection system of the transformer substation is arranged integrated in the same high-voltage switchgear, such as, for example, electronic relays and measurement and control means associated with said electronic relays, such as, for example, voltage sensors, intensity sensors, voltage transformers, means for receiving/transmitting signals via PLC, means for detecting partial discharges, etc.
As is known, electronic relays and the measurement and control means associated therewith form the intelligent part of transformer substations, i.e., they form an integral protection unit preventing disturbances of the high-voltage and low-voltage network, by isolating a transformer substation in a malfunction. In current transformer substations, the fuse itself is the protection for said substations. The fuse protects the equipment, and if malfunctions of another type not protected by the fuse are to be seen, a relay combined or associated with the fuses can be provided. Likewise, the breaker or switch also acts under the orders of the electronic relay, which orders the opening of said breaker or switch as a consequence of a fault event.